1. Field of the Invention
The present invention relates generally to boiling water reactors and, more particularly, to a method and apparatus for repairing welds in a boiling water reactor shroud.
2. Discussion of the Related Art
Boiling water reactor shrouds are disposed concentrically within reactor vessels to divide the flow of coolant water through the reactor vessels and to structurally support and align the fuel assemblies, steam separator assemblies and control rod guide tubes. The shrouds are generally cylindrical and are typically formed of multiple arcuate steel plates joined by welds along their abutting vertical and horizontal edges. After periods of use, cracking of the shroud within heat affected zones of the welds tends to occur as a result of corrosion, radiation and stress. When excessive cracking of the welds occurs, the shroud must either be replaced or repaired.
U.S. Pat. No. 5,402,570 to Weems et al, the disclosure of which is incorporated herein by reference, describes a method of repairing boiling water reactor core shrouds having horizontal cracks in heat affected zones of welds by securing plural tie rods in vertical orientation about the periphery of the cracked shroud to axially compress the shroud and thereby urge the opposing surfaces of the horizontal cracks toward one another. Lateral or radial spacers or bumpers may also be installed between the inner surface of the reactor vessel and the outer surface of the shroud and/or tie rods to resist horizontal seismic loads and to hold the shroud in place relative to the vessel wall in the event of cracking along any horizontal weld during a seismic event.
While the tie rod repair described in U.S. Pat. No. 5,402,570 provides an acceptable method for mitigating the consequences of cracking along horizontal welds, there exists a need for a vertical weld repair which can be used alone or in combination with tie rods to mitigate the consequences of cracking along vertical welds in a boiling water reactor core shroud.